Codewars Kata SQL

Simple Fun #74: Growing Plant

Task

Each day a plant is growing by upSpeed meters. Each night that plant's height decreases by downSpeed meters due to the lack of sun heat. Initially, plant is 0 meters tall. We plant the seed at the beginning of a day. We want to know when the height of the plant will reach a certain level.

Example

For upSpeed = 100, downSpeed = 10 and desiredHeight = 910, the output should be 10.

After day 1 --> 100
 After night 1 --> 90
 After day 2 --> 190
 After night 2 --> 180
 After day 3 --> 280
 After night 3 --> 270
 After day 4 --> 370
 After night 4 --> 360
 After day 5 --> 460
 After night 5 --> 450
 After day 6 --> 550
 After night 6 --> 540
 After day 7 --> 640
 After night 7 --> 630
 After day 8 --> 730
 After night 8 --> 720
 After day 9 --> 820
 After night 9 --> 810
 After day 10 --> 910

For upSpeed = 10, downSpeed = 9 and desiredHeight = 4, the output should be 1.

Because the plant reach to the desired height at day 1(10 meters).

After day 1 --> 10

Input/Output

Input

-----------------------------------------
|     Table     |    Column      | Type |
|---------------+----------------+------|
| growing_plant | down_speed     | int  |
|               | up_speed       | int  |
|               | desired_height | int  |
-----------------------------------------

Columns

• up_speed: A positive integer representing the daily growth. Constraints: 5 ≤ up_speed ≤ 100.
• down_speed: A positive integer representing the nightly decline. Constraints: 2 ≤ down_speed < up_speed.
• desired_height: A positive integer representing the threshold. Constraints: 4 ≤ desired_height ≤ 1000.

Output

-------------------
|  Column  | Type |
|----------+------|
| id       | int  |
| num_days | int  |
-------------------

num_days is the number of days that it will take for the plant to reach/pass desiredHeight (including the last day in the total count).

Solution:

SELECT id, 
  CASE WHEN desired_height <= up_speed THEN 1
  ELSE CEIL((desired_height - up_speed)::decimal / (up_speed - down_speed))::int + 1 END AS num_days
FROM growing_plant;

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